Although not natively portable (yet? See below), X2Go (https://wiki.x2go.org/) looks like an exciting new Python based free solution for remote access to Linux desktops, with clients available for all major platforms.

[url]https://wiki.x2go.org/doku.php/doc:newtox2go[/url] author wrote:X2Go is a Remote Desktop solution, which some vendors vaguely call Remote Control. This is not to be confused with Microsoft Remote Desktop Connection, which is a competing Remote Desktop solution and protocol. With X2Go, you mainly access Linux computers. The Linux computer you are accessing is the X2Go Server. (There are ways to connect to a Windows computer as well; some of them are only available with the Linux X2Go Client.)

A procedure is available to use X2Go Windows (32-bit) client without admin privileges (untested!):

[url]https://wiki.x2go.org/doku.php/doc:installation:x2goclient[/url] author wrote:To install X2Go Client without admin rights (and without a start menu entry or an entry in “add/remove programs”):
[*] Open the X2Go Client setup.exe in an archive manager such as 7-zip.
[*] Extract all the contents to a new folder of your choosing. Let's assume this folder is called "x2goclient".
[*] Move the "pulse" and "VcXsrv" folders from under 'x2goclient/$_OUTDIR\' to directly under 'x2goclient/' .
[*] Delete the 'x2goclient/$PLUGINSDIR\' folder and the 'x2goclient/$_OUTDIR\' folder.
[*] Once finished, your main folder should have dozens of files directly in it, the "pulse" subfolder, and the "VcXsrv" subfolder.